Ionization of CH4 under fast He-like Si-ion impact

Abstract

We have studied the absolute double differential cross section (DDCS) of electrons ejected from the methane molecule (CH${}_4$) under the impact of highly charged fast projectile ions. The energy and angular distributions of electrons have been measured in interactions with 70 MeV Si${}^{12+}$ ions. These DDCS data together with the derived single differential cross sections and the total cross section (TCS) have been compared with predictions of the continuum distorted wave-eikonal initial state model using different approaches for the molecular orbitals. It has been found that the theories overestimate the measured DDCS values at low ejection energies, which may indicate shortcomings of the model in the case of strong perturbation. At the same time, applying the model to a previous measurement using fast C ions having a lower perturbation strength, excellent agreements have been obtained with the experimental data. Considering the scaling properties, the available TCS data have been plotted with a scaled parameter, namely the perturbation strength, q/v (where q= charge state, v=velocity of the projectile). The KLL Auger e-emission as well as the KLL hyper-satellite peaks are analyzed for different emission angles. The double K-vacancy production shows a considerable enhancement i.e. 37% of the single production cross section which is consistent with some of the recent experiments on K-ionization using x-ray techniques.